Gas turbine engines typically include a rotor assembly, a compressor, and a turbine. In turbofan engines, the rotor assembly includes a fan having an array of fan blades extending radially outwardly from a rotor shaft. The rotor shaft, which transfers power and rotary motion from the turbine to both the compressor and the fan, is supported longitudinally using a plurality of bearing assemblies. Known bearing assemblies include one or more rolling elements supported within a paired race. To maintain a rotor critical speed margin, the rotor assembly is typically supported on three bearing assemblies: one thrust bearing assembly and two roller bearing assemblies. The thrust bearing assembly supports the rotor shaft and minimizes axial and radial movement thereof, while the roller bearing assemblies support radial movement of the rotor shaft.
Usually, these bearing assemblies include dampers, e.g., for damping rotor vibrations. A common damper is a fluid film or squeeze film damper, which provides a thin film of a lubricant, such as oil, within the bearing assembly that resists whirling and/or other motion of the bearing, e.g., to compensate for rotor imbalance and dissipate rotor vibrations. Such dampers function best when the lubricant has a relatively low viscosity, e.g., when the oil is relatively warm. However, when the lubricant is cold (for instance, due to a cold engine or low ambient air temperatures), it is relatively highly viscous and negatively impacts the performance of the damper. Therefore, it is common to require the engine to idle for a specified amount of time upon a cold engine start or in-flight re-start to allow the lubricant to warm up such that the dampers may perform as intended. Further, the dampers may be designed to compensate for cold lubricant conditions, such that known damper designs are sub-optimal.
Accordingly, a bearing damper for a gas turbine engine that allows reduction or elimination of time-at-idle and/or optimization of the damper configuration would be welcomed in the technology.